The emission of carbon dioxide (CO2) and other polluting gases from the burning of fossil fuels has received worldwide attention because of its implication in climate change, which threatens economies and environments. Accordingly, intensive research continues in the search for new materials that can efficiently, reversibly, and economically capture CO2 and other polluting gases. Numerous carbon capture and storage (CCS) technologies have been developed, including post-combustion CO2 capture using amine solvents, oxy-fuel combustion, and integrated gasification combined cycles (IGCC). Among these, post-combustion CO2 capture using aqueous amine-based systems have been relied upon as the most practical short term solution due to the relatively high CO2/N2 selectivity, ability to function in the presence of water, high reactivity, and low absorbent cost. However, such amine-based systems have significant drawbacks including solvent loss, corrosion, and most importantly, intensive energy demand for regeneration.
Ionic liquids (ILs) are particularly attractive candidates for capture of carbon dioxide (CO2) and other polluting gases because of their unique properties, such as low or negligible vapor pressures, wide liquid temperature ranges, generally high thermal stabilities, and tunable properties. However, current processes using ionic liquids for this purpose (typically, amino-functionalized ILs) are beset with several drawbacks. A particular problem associated with many current IL capture materials is the high viscosity generated in these ILs on absorbing CO2. This substantial rise in viscosity adversely slows absorption kinetics, and hence, substantially increases operating costs. There are indications that the rise in viscosity in such ILs can be attributed to strong and dense hydrogen-bond networks during the reaction of CO2 with the IL (e.g., Gutowski, K. E., et al., J. Am. Chem. Soc., 2008, 130, 14690-14704). This increased viscosity hinders mass transfer, effectively slowing the sorption and desorption kinetics of the ionic liquid. Moreover, current IL materials generally possess subpar CO2 absorption capacities and absorption rates for CO2 capture.